<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>lesson 23</title>
  <style>
    .transition {
      transition: 3s background-color ease;
    }
  </style>
  <script src="https://unpkg.com/vue@next"></script>
</head>

<body>
  <div id="root"></div>
</body>
<script>
  const app = Vue.createApp({
    data() {
      return {
        styleObj: {
          background: 'blue'
        }
      }
    },
    methods: {
      handleClick() {
        if (this.styleObj.background === 'blue') {
          this.styleObj.background = 'green';
        } else {
          this.styleObj.background = 'blue'
        }
      }
    },
    template: `
      <div>
        <div class="transition" :style="styleObj">hello world</div>
        <button @click="handleClick">切换</button>
      </div>
    `
  });

  const vm = app.mount('#root');
</script>

</html>